1. Field of the Invention
The invention pertains to a transparent cover layer of soft elastic polyurethane for viewing windows or other transparent glass or plastic substrates, with a condensation-inhibiting effect.
2. Background of the Prior Art
Transparent soft elastic cover layers with a condensation-inhibiting effect are the object of the German patent application P 37 04 294. On the one hand, they have the property of undergoing plastic deformation, which returns to the original state after a short period of time, under the usual type of stress, which would result in surface deformations and scratches in harder plastics. On the other hand, they have the advantage of demonstrating a marked condensation-inhibiting effect. The condensation-inhibiting effect is based on a synergistic effect of sulfonated polyether polyol, i.e. polyether polyol containing sulfonate groups, and a non-ionic polyether polysiloxane which as present as the same time, to which the reaction mixture which forms polyurethane is added.
The condensation-inhibiting effect of these known cover layers is absolutely satisfactory at average temperatures. At temperatures below +10 degrees Celsius and after extended contact with water, however, the condensation-inhibiting effect is not completely satisfactory at higher requirements.